A.S/NB.C/AC.C/ID.C/N
A.40ΩB.60ΩC.70ΩD.50Ω
A.電源沒(méi)打開(kāi)B.電源打開(kāi)且正常C.正在發(fā)送數(shù)據(jù)D.未發(fā)送數(shù)據(jù)